On-press developable thermosensitive lithographic printing plates

ABSTRACT

This patent describes an on-press ink and/or fountain solution developable lithographic printing plates having on a substrate a thermosensitive layer capable of hardening upon exposure to an infrared radiation. The plate can be imagewise exposed with an infrared radiation and then on-press developed with ink and/or fountain solution by rotating the plate cylinder and engaging ink and/or fountain solution roller. The developed plate can then directly print images to the receiving sheets. The imagewise exposure can be performed off the press or with the plate being mounted on the plate cylinder of a lithographic press.

RELATED PATENT APPLICATIONS

[0001] This application is a continuation-in-part of my U.S. patentapplication Ser. Nos. 09/656,052 filed Sep. 6, 2000, 09/873,598 filedJun. 4, 2001, and 09/952,933 filed Sep. 14, 2001.

FIELD OF THE INVENTION

[0002] This invention relates to lithographic printing plates. Moreparticularly, it relates to on-press ink and/or fountain solutiondevelopable lithographic plates having on a substrate a thermosensitivelayer capable of hardening upon exposure to an infrared laser radiation.

BACKGROUND OF THE INVENTION

[0003] Lithographic printing plates (after process) generally consist ofink-receptive areas (image areas) and ink-repelling areas (non-imageareas). During printing operation, an ink is preferentially received inthe image areas, not in the non-image areas, and then transferred to thesurface of a material upon which the image is to be produced. Commonlythe ink is transferred to an intermediate material called printingblanket, which in turn transfers the ink to the surface of the materialupon which the image is to be produced.

[0004] Lithographic printing can be further divided into two generaltypes: wet lithographic printing (conventional lithographic printing)and waterless lithographic printing. In wet lithographic printingplates, the ink-receptive areas consist of oleophilic materials and theink-repelling areas consist of hydrophilic materials; fountain solution(consisting of primarily water) is required to continuously dampen thehydrophilic materials during printing operation to make the non-imageareas oleophobic (ink-repelling). In waterless lithographic printingplates, the ink-receptive areas consist of oleophilic materials and theink-repelling areas consist of oleophobic materials; no dampening withfountain solution is required.

[0005] At the present time, lithographic printing plates (processed) aregenerally prepared from lithographic printing plate precursors (alsocommonly called lithographic printing plates) comprising a substrate anda photosensitive coating deposited on the substrate, the substrate andthe photosensitive coating having opposite surface properties (such ashydrophilic vs. oleophilic, and oleophobic vs. oleophilic). Thephotosensitive coating is usually a photosensitive material, whichsolubilizes or hardens upon exposure to an actinic radiation, optionallywith further post-exposure overall treatment. Here, hardening meansbecoming insoluble in a certain developer. In positive-working systems,the exposed areas become more soluble and can be developed to reveal theunderneath substrate. In negative-working systems, the exposed areasbecome hardened and the non-exposed areas can be developed to reveal theunderneath substrate. The exposed plate is usually developed with aliquid developer to bare the substrate in the non-hardened areas.

[0006] On-press developable lithographic printing plates have beendisclosed in the literature. Such plates can be directly mounted onpress after exposure to develop with ink and/or fountain solution duringthe initial press operation and then to print out regular printedsheets. No separate development process before mounting on press isneeded. Among the patents describing on-press developable lithographicprinting plates are U.S. Pat. Nos. 5,258,263, 5,516,620, 5,561,029,5,616,449, 5,677,110, 5,811,220, 6,014,929, 6,071,675, and 6,242,156.

[0007] Conventionally, the plate is exposed with an actinic light(usually an ultraviolet light from a lamp) through a separate photomaskfilm having predetermined image pattern that is placed between the lightsource and the plate. While capable of providing plate with superiorlithographic quality, such a method is cumbersome and labor intensive.

[0008] Laser sources have been increasingly used to imagewise expose aprinting plate that is sensitized to a corresponding laser wavelength.This allows the elimination of the photomask film, reducing material,equipment and labor cost.

[0009] Among the laser imagable plates, infrared laser sensitive platesare the most attractive because they can be handled and processed underwhite light. Infrared laser sensitive plates are also calledthermosensitive plates or thermal plates because the infrared laser isusually converted to heat to cause a certain chemical or physical change(such as hardening, solubilization, ablation, phase change, or thermalflow) needed for plate making (although in some systems certain electronor energy transfers from the infrared dye to the initiator may also takeplace).

[0010] Various thermosensitive plates have been disclosed in the patentliterature. Examples of thermosensitive plates are described in U.S.Pat. Nos. 4,054,094 and 5,379,698 (laser ablation plates), 5,705,309,5,674,658, 5,677,106, 6,153,356, 6,232,038, and 4,997,745 (negativethermosensitive plates), 5,491,046 and 6,117,610 (both positive andnegative thermosensitive plates, depending on the process), and5,919,600 and 5,955,238 (thermosensitive positive waterless plate).

[0011] Despite the progress in conventional on-press developable platesand digital laser imagable plates, there is a desire for a lithographicplate which can be imaged by infrared laser, does not produce ablationdebris, and does not require a separate liquid development process. Morespecifically, there is a desire for a thermosensitive lithographic platethat is on-press developable with ink and/or fountain solution.

SUMMARY OF THE INVENTION

[0012] It is an object of this invention to provide a thermosensitivelithographic plate which is imagable with an infrared radiation(including infrared laser) and on-press developable with ink and/orfountain solution.

[0013] It is another object of this invention to provide an on-pressdevelopable thermosensitive lithographic plate having on a substrate athermosensitive layer comprising a polymerizable monomer, an initiator,and an infrared absorbing dye or pigment.

[0014] It is yet another object of this invention to provide a method ofon-press development or on-press imaging and development of the abovelithographic plate.

[0015] Further objects, features and advantages of the present inventionwill become apparent from the detailed description of the preferredembodiments.

[0016] According to the present invention, there has been provided anegative lithographic printing plate capable of on-press developmentwith ink and/or fountain solution, comprising on a substrate athermosensitive layer, said thermosensitive layer being capable ofhardening upon exposure to an infrared radiation and on-pressdevelopable with ink and/or fountain solution; wherein at least thehardened areas of said thermosensitive layer exhibit an affinity oraversion substantially opposite to the affinity or aversion of saidsubstrate to at least one printing liquid selected from the groupconsisting of ink and an abhesive fluid for ink. The on-pressdevelopable lithographic plate is achieved or improved by variousembodiments as described below:

[0017] (a) utilizing a thermosensitive layer comprising (i) a cationicpolymerizable monomer, (ii) a cationic initiator, and (iii) an infraredabsorber;

[0018] (b) utilizing a thermosensitive layer comprising (i) a freeradical polymerizable monomer, (ii) a free radical initiator, (iii) aninfrared absorbing dye;

[0019] (c) coating the thermosensitive layer conformally on a roughenedsubstrate so that the surface of the thermosensitive layer has peaks andvalleys substantially corresponding to the major peaks and valleys ofthe substrate microscopic surface;

[0020] (d) adding a nonionic surfactant at higher concentration (1.0 to30% by weight) into the thermosensitive layer;

[0021] (e) coating a thin overcoat (0.001 to 0.450 g/m²) on thethermosensitive layer;

[0022] (f) insert a releasable interlayer between the thermosensitivelayer and the substrate; and

[0023] (g) utilizing a cationic or free radical polymerizablethermosensitive layer comprising hydrophilic salt groups; saidthermosensitive layer being hydrophilic, and capable of hardening andbecoming oleophilic upon exposure to an infrared radiation.

[0024] This invention also describes on-press development, and on-pressimaging and development of the above lithographic plates.

[0025] The plate can be imagewise exposed with an infrared radiation ona plate exposure device and then transferred to a lithographic press foron-press development with ink and/or fountain solution by rotating theplate cylinder and engaging ink and/or fountain solution roller. Thedeveloped plate can then directly print images to the receiving sheets.Alternatively, the plate can be imagewise exposed with an infraredradiation while mounted on a plate cylinder of a lithographic press,on-press developed on the same press cylinder with ink and/or fountainsolution, and then directly print images to the receiving sheets.Infrared laser is a preferred infrared radiation.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The substrate employed in the lithographic plates of thisinvention can be any lithographic support. Such a substrate may be ametal sheet, a polymer film, or a coated paper. Aluminum (includingaluminum alloys) sheet is a preferred metal support. Particularlypreferred is an aluminum support that has been grained, anodized, anddeposited with a barrier layer. Polyester film is a preferred polymericfilm support. A surface coating may be coated to achieve desired surfaceproperties. For wet plate, the substrate should have a hydrophilic oroleophilic surface, depending on the surface properties of thethermosensitive layer; commonly, a wet lithographic plate has ahydrophilic substrate and an oleophilic thermosensitive layer. Forwaterless plate, the substrate should have an oleophilic or oleophobicsurface, depending on the surface properties of the thermosensitivelayer.

[0027] Particularly preferred hydrophilic substrate for a wetlithographic plate is an aluminum support that has been grained,anodized, and deposited with a hydrophilic barrier layer. Surfacegraining (or roughening) can be achieved by mechanical graining orbrushing, chemical etching, and/or AC electrochemical graining. Theroughened surface can be further anodized to form a durable aluminumoxide surface using an acid electrolyte such as sulfuric acid and/orphosphoric acid. The roughened and anodized aluminum surface can befurther thermally or electrochemically coated with a layer of silicateor hydrophilic polymer such as polyvinyl phosphonic acid,polyacrylamide, polyacrylic acid, polybasic organic acid, copolymers ofvinyl phosphonic acid and acrylamide to form a durable hydrophiliclayer. Polyvinyl phosphonic acid and its copolymers are preferredpolymers. Processes for coating a hydrophilic barrier layer on aluminumin lithographic plate application are well known in the art, andexamples can be found in U.S. Pat. Nos. 2,714,066, 4,153,461, 4,399,021,and 5,368,974. Suitable polymer film supports for a wet lithographicplate include a polymer film coated with a hydrophilic layer, preferablya hydrophilic layer that is crosslinked, as described in U.S. Pat. No.5,922,502.

[0028] For preparing printing plates of the current invention, anythermosensitive layer is suitable which is capable of hardening throughpolymerization or crosslinking upon exposure to an infrared radiation(about 700 to 1500 nm in wavelength), and is soluble or dispersible inand on-press developable with ink (for waterless plate) or ink and/orfountain solution (for wet plate). Here hardening means becominginsoluble and non-dispersible in ink and/or fountain solution, and isachieved through polymerization or crosslinking of the resins (monomers,oligomers, or polymers). An infrared absorbing dye or pigment is usuallyused in the thermosensitive layer as sensitizer or light-to-heatconverter. The thermosensitive layer preferably has a coverage of from100 to 4000 mg/m², and more preferably from 400 to 2000 mg/m².

[0029] It is noted that the thermosensitive layer can be a single layerwith substantially homogeneous composition along the depth. However, thethermosensitive layer can consist of more than one sublayers havingdifferent compositions (such as different resins) or different materialratios in each layer (such as higher infrared dye amount in the innerlayer than the top layer). The thermosensitive layer may also havecomposition gradient along the depth (such as lower infrared dye amounttoward the surface and higher infrared dye amount toward the substrate).

[0030] Thermosensitive layer suitable for the current invention may beformulated from various thermosensitive materials containing an infraredabsorbing dye or pigment. The composition ratios (such as monomer topolymer ratio) are usually different from conventional plates designedfor development with a regular liquid developer. Various additives maybe added to, for example, allow or enhance on-press developability. Suchadditives include surfactant, plasticizer, water-soluble polymer orsmall molecule, and ink soluble polymer or small molecule. The additionof nonionic surfactant is especially helpful in making thethermosensitive layer dispersible with ink and fountain solution, oremulsion of ink and fountain solution. Various additives useful forconventional thermosensitive layer can also be used. These additivesinclude pigment, dye, exposure indicator, and stabilizer.

[0031] Thermosensitive materials useful in negative-working wet platesof this invention include, for example, thermosensitive compositionscomprising a polymerizable monomer, thermosensitive initiator, andinfrared light absorbing dye or pigment.

[0032] It is noted that, in this patent, the term monomer includes bothmonomer and oligomer, and the term (meth)acrylate includes both acrylateand methacrylate.

[0033] In a preferred embodiment as for negative-working wetlithographic printing plates of this invention, the thermosensitivelayer comprises at least one epoxy or vinyl ether monomer having atleast one epoxy or vinyl ether functional group, at least one Bronstedacid generator capable of generating free acid in the presence of aninfrared absorbing dye or pigment upon exposure to an infraredradiation, and at least one infrared absorbing dye or pigment,optionally with one or more polymeric binders. Other additives such assurfactant, dye or pigment, exposure-indicating dye (such as leucocrystal violet, azobenzene, 4-phenylazodiphenylamine, and methylene bluedyes), and acid quencher (usually an alkaline compound, such astetrabutylammonium hydroxide or triethylamine) may be added.

[0034] In a second preferred embodiment as for negative-working wetlithographic printing plates of this invention, the thermosensitivelayer comprises at least one polymerizable ethylenically unsaturatedmonomer having at least one terminal ethylenic group, at least onefree-radical initiator capable of generating free radical in thepresence of an infrared absorbing dye or pigment upon exposure to aninfrared radiation, and at least one infrared absorbing dye or pigment,optionally with one or more polymeric binders. Other additives such assurfactant, dye or pigment, exposure-indicating dye (such as leucocrystal violet, leucomalachite green, azobenzene,4-phenylazodiphenylamine, and methylene blue dyes), and free-radicalstabilizer (such as methoxyhydroquinone) may be added. It is noted thatcertain additives can significantly reduce the polymerization rate of afree radical polymerization system sensitized by an infrared absorbingdye and should be avoided or used at minimum.

[0035] In a third preferred embodiment as for negative-working wetlithographic printing plates of this invention, the thermosensitivelayer contains both free radical and cationic polymerization systems.The thermosensitve layer can comprise an ethylenically unsaturatedmonomer, a free-radical initiator, an epoxy or vinyl ether monomer, aBronsted acid generator, and an infrared absorbing dye or pigment,optionally with one or more polymeric binders. Various other additivesmay be added. The ethylenically unsaturated monomer and the epoxy orvinyl ether functional monomer can be the same compound wherein thecompound contains both ethylenic group and epoxy or vinyl ether group.Examples of such compounds include epoxy functional acrylic monomers,such as glycidyl acrylate. The free radical initiator and the cationicinitiator can be the same compound if the compound is capable ofgenerating both free radical and free acid. Examples of such compoundsinclude various onium salts such as diaryliodonium hexafluoroantimonateand s-triazines such as2,4-bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen-1-yl]-s-triazinewhich are capable of generating both free radical and free acid in thepresence of an infrared dye or pigment upon exposure to an infraredradiation.

[0036] Suitable free-radical polymerizable monomers include, forexample, multifunctional (meth)acrylate monomers (such as (meth)acrylateesters of ethylene glycol, trimethylolpropane, pentaerythritol,ethoxylated ethylene glycol and ethoxylated trimethylolpropane,multifunctional urethanated (meth)acrylate, and epoxylated(meth)acrylate), and oligomeric amine diacrylates. The (meth)acrylicmonomers may also have other double bond or epoxide group, in additionto (meth)acrylate group. The (meth)acrylate monomers may also contain anacidic (such as carboxylic acid) or basic (such as amine) functionality.

[0037] Any free radical initiator capable of generating free radical inthe presence of an infrared absorbing dye or pigment upon exposure to aninfrared radiation can be used as the thermosensitive free radicalinitiator of this invention. Suitable free-radical initiators include,for example, the derivatives of acetophenone (such as2,2-dimethoxy-2-phenylacetophenone, and2-methyl-1-[4-(methylthio)phenyl]-2-morpholino propan-1-one);benzophenone; benzil; ketocoumarin (such as 3-benzoyl-7-methoxy coumarinand 7-methoxy coumarin); xanthone; thioxanthone; benzoin or analkyl-substituted anthraquinone; onium salts (such as diaryliodoniumhexafluoroantimonate, diaryliodonium triflate,(4-(2-hydroxytetradecyl-oxy)-phenyl)phenyliodonium hexafluoroantimonate,triarylsulfonium hexafluorophosphate, triarylsulfoniump-toluenesulfonate, (3-phenylpropan-2-onyl) triaryl phosphoniumhexafluoroantimonate, and N-ethoxy(2-methyl)pyridiniumhexafluorophosphate, and onium salts as described in U.S. Pat. Nos.5,955,238, 6,037,098, and 5,629,354); borate salts (such astetrabutylammonium triphenyl(n-butyl)borate, tetraethylammoniumtriphenyl(n-butyl)borate, diphenyliodonium tetraphenylborate, andtriphenylsulfonium triphenyl(n-butyl)borate, and borate salts asdescribed in U.S. Pat. Nos. 6,232,038 and 6,218,076,); haloalkylsubstituted s-triazines (such as2,4-bis(trichloromethyl)-6-(p-methoxy-styryl)-s-triazine,2,4-bis(trichloromethyl)-6-(4-methoxy-naphth-1-yl)-s-triazine,2,4-bis(trichloromethyl)-6-piperonyl-s-triazine, and2,4-bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen-1-yl]-s-triazine,and s-triazines as described in U.S. Pat. Nos. 5,955,238, 6,037,098,6,010,824, and 5,629,354); and titanocene(bis(η⁹-2,4-cyclopentadien-1-yl)bis[2,6-difluoro-3-(1H-pyrrol-1-yl)phenyl) titanium). Onium salts,borate salts, and s-triazines are preferred thermosensitive free radicalinitiators. Diaryliodonium salts and triarylsulfonium salts arepreferred onium salts. Triarylalkylborate salts are preferred boratesalts. Trichloromethyl substituted s-triazines are preferreds-triazines.

[0038] Suitable polyfunctional epoxy monomers include, for example,3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexane carboxylate,bis-(3,4-epoxycyclohexymethyl) adipate, difunctional bisphenolA/epichlorohydrin epoxy resin and multifunctionalepichlorohydrin/tetraphenylol ethane epoxy resin.

[0039] Suitable cationic photoinitiators include, for example,triarylsulfonium hexafluoroantimonate, triarylsulfoniumhexafluorophosphate, diaryliodonium hexafluoroantimonate, and haloalkylsubstituted s-triazine. It is noted that most cationic initiators arealso free radical initiators because, in addition to generating Bronstedacid, they also generate free radicals during photo or thermaldecomposition.

[0040] Infrared absorbers useful in the thermosensitive layer of thisinvention include any infrared absorbing dye or pigment effectivelyabsorbing an infrared radiation having a wavelength of 700 to 1,500 nm.It is preferable that the dye or pigment having an absorption maximumbetween the wavelengths of 750 and 1,200 nm. Various infrared absorbingdyes or pigments are described in U.S. Pat. Nos. 5,858,604, 5,922,502,6,022,668, 5,705,309, 6,017,677, and 5,677,106, and in the book entitled“Infrared Absorbing Dyes” edited by Masaru Matsuoka, Plenum Press, NewYork (1990), and can be used in the thermosensitive layer of thisinvention. Examples of useful infrared absorbing dyes includesquarylium, croconate, cyanine (including polymethine), phthalocyanine(including naphthalocyanine), merocyanine, chalcogenopyryloarylidene,oxyindolizine, quinoid, indolizine, pyrylium and metal dithiolene dyes.Cyanine and phthalocyanine dyes are preferred infrared absorbing dyes.Examples of useful infrared absorbing pigments include black pigments,metal powder pigments, phthalocyanine pigments, and carbon black. Carbonblack is a preferred infrared absorbing pigment. Mixtures of dyes,pigments, or both can also be used. Infrared absorbing dye is preferredover infrared absorbing pigment because the infrared absorbing dyeusually has higher absorbing efficiency, gives less visible color, andallows molecular level charge or energy transfer to activate theinitiator. The infrared dye or pigment is added in the thermosensitivelayer preferably at 0.01 to 30% by weight of the thermosensitive layer,more preferably at 0.1 to 20%, and most preferably at 0.5 to 10%.

[0041] While a thermosensitive layer generally comprises an infraredabsorbing dye or pigment, the infrared dye moiety may also beincorporated into the molecules of the initiator, monomer, oligomer, orpolymer. For example, infrared dye moieties are incorporated into thepolymer of a thermosensitive layer for a waterless lithographic plate asdescribed in U.S. Pat. No. 6,132,933. Clearly, this polymer can functionas both polymeric binder and infrared absorbing dye.

[0042] Suitable polymeric binders for the thermosensitive layers of thisinvention include, for example, polystyrene, (meth)acrylic polymers andcopolymers (such as polybutylmethacrylate, polyethylmethacrylate,polymethylmethacrylate, polymethylacrylate,butylmethacrylate/methylmethacrylate copolymer), polyvinyl acetate,polyvinyl chloride, styrene/acrylonitrile copolymer, nitrocellulose,cellulose acetate butyrate, cellulose acetate propionate, vinylchloride/vinyl acetate copolymer, partially hydrolyzed polyvinylacetate, polyvinyl alcohol partially condensation-reacted withacetaldehyde, butadiene/acrylonitrile copolymer, and polyurethanebinder. Also useful are aqueous alkaline soluble polymers, such as(meth)acrylic polymer with substantial number of carboxylic acidfunctional groups, polymer with substantial number of phenol groups, andpolymer with (meth)acrylate groups and carboxylate salt groups asdescribed in U.S. Pat. No. 5,849,462. For oleophilic thermosensitivelayers, preferred polymeric binders are aqueous alkaline-insolubleoleophilic polymers. The polymers may or may not have polymerizablefunctional groups (such as ethylenic group, epoxy group, or vinyl ethergroup).

[0043] Various surfactants may be added into the thermosensitive layerto allow or enhance the on-press ink and/or fountain solutiondevelopability. Both polymeric and small molecule surfactants can beused. However, it is preferred that the surfactant has low or novolatility so that it will not evaporate from the thermosensitive layerof the plate during storage and handling. Nonionic surfactants arepreferred. The nonionic surfactant used in this invention should havesufficient portion of hydrophilic segments (or groups) and sufficientportion of oleophilic segments (or groups), so that it is at leastpartially soluble in water (>1 g surfactant soluble in 100 g water) andat least partially soluble in organic phase (>1 g surfactant soluble in100 g thermosensitive layer). Preferred nonionic surfactants arepolymers and oligomers containing one or more polyether (such aspolyethylene glycol, polypropylene glycol, and copolymer of ethyleneglycol and propylene glycol) segments. Examples of preferred nonionicsurfactants are block copolymers of propylene glycol and ethylene glycol(also called block copolymer of propylene oxide and ethylene oxide);ethoxylated or propoxylated acrylate oligomers; and polyethoxylatedalkylphenols and polyethoxylated fatty alcohols. The nonionic surfactantis preferably added at from 0.1 to 30% by weight of the thermosensitivelayer, more preferably from 0.5 to 20%, and most preferably from 1 to15%.

[0044] A particulate dispersion may be added into the thermosensitivelayer to enhance, for example, the developability and non-tackiness ofthe plate, as described in U.S. Pat. No. 6,071,675, the entiredisclosure of which is hereby incorporated by reference.

[0045] When a photoinitiator is used as the free acid or free radicalinitiator in the thermosensitive layer, the photoinitiator can besensitive to ultraviolet light (or even visible light), or can be onlysensitive to light of shorter wavelength, such as lower than 350 nm.Thermosensitive layer containing ultraviolet light (or visible light)sensitive photoinitiator will also allow actinic exposure withultraviolet light (or visible light). Thermosensitive layer containingphotoinitiator only sensitive to shorter wavelength (such as shorterthan 350 nm) will have good white light stability. Each type ofinitiators has its own advantage, and can be used to design a specificproduct. In this patent, all types of photoinitiators can be used.

[0046] The hardened areas of the thermosensitive layer should exhibit anaffinity or aversion substantially opposite to the affinity or aversionof the substrate to at least one printing liquid selected from the groupconsisting of ink and an abhesive fluid for ink. An abhesive fluid forink is a fluid that repels ink. Fountain solution is the most commonlyused abhesive fluid for ink. A wet plate is printed on a wet pressequipped with both ink and fountain solution, while a waterless plate isprinted on a waterless press equipped with ink.

[0047] The thermosensitive layer useful for the plate of this inventionusually has substantially the same affinity or aversion before and afterexposure. However, an on-press developable thermosensitive layer thatchanges affinity or aversion dramatically upon exposure so that it hasaffinity or aversion similar to the substrate before exposure andopposite to the substrate after exposure can also be used for thelithographic plate of this invention. For example, a plate can have ahydrophilic substrate and an ink and/or fountain solution soluble ordispersible hydrophilic thermosensitive layer that is capable ofhardening and becoming oleophilic upon exposure to an infrared laser.While such a thermosensitive layer is more complicated in composition,it has the advantage that the non-hardened areas do not need to becompletely developed off very quickly during the initial printingprocess. The non-hardened areas can act as the hydrophilic areas of theplate for initial lithographic printing and gradually be developed offto reveal the hydrophilic substrate that will act as the permanenthydrophilic areas of the plate. The change in affinity or aversion ofthe thermosensitive layer upon infrared laser irradiation can beachieved by, for example, loss of a hydrophilic functional group such asdecomposition of salt functional groups, or crosslinking of resins withsalt functional groups so that the penetration of water to thethermosensitive layer is minimized.

[0048] A preferred thermosensitive layer of such a plate comprises apolymer having thermally decomposable salt functional groups, a freeradical polymerizable ethylenically unsaturated monomer, a free-radicalinitiator, and an infrared absorbing dye. A second preferredthermosensitive layer of such a plate comprises a free radicalpolymerizable ethylenically unsaturated monomer having thermallydecomposible salt functional groups, a free-radical initiator, and aninfrared absorbing dye. Here the thermosensitive layer is hydrophilic,soluble or dispersible in ink and/or fountain solution, and capable ofhardening and becoming oleophilic upon exposure to an infraredradiation. Regular monomer, oligomer, or polymer that does not have saltfunctional groups, and various additives such as pigment, dye, exposureindicator, and surfactant can be added into the thermosensitive layer.Suitable salt functional groups are described in U.S. Pat. Nos.6,190,830, 6,190,831, and 6,159,657, and can be used for the saltfunctional groups containing polymer, monomer or oligomer of thisinvention. Examples of suitable salt functional groups includeorganoonium groups (such as organoammonium, organophosphonium, andorganosulfonium groups), N-alkylated aromatic heterocyclic groups,carboxylate salt groups (such as tetraalkylammonium carboxylate groups),sulfonate salt groups (such as sulfonic acid triethylamine salt).

[0049] The thermosensitive layer may be conformally coated onto aroughened substrate (for example, with Ra of larger than 0.4micrometers) at thin coverage (for example, of less than 1.5 g/m²) sothat the plate can have microscopic peaks and valleys on thethermosensitive layer coated surface and exhibit low tackiness and goodblock resistance, as described in U.S. Pat. No. 6,242,156, the entiredisclosure of which is hereby incorporated by reference. Here thesubstrate has a roughened surface comprising peaks and valleys, and thethermosensitive layer is substantially conformally coated on theroughened substrate surface so that the surface of the thermosensitivelayer has peaks and valleys substantially corresponding to the majorpeaks and valleys of the substrate microscopic surface. In a preferredembodiment, the substrate has an average surface roughness Ra of about0.2 to about 2.0 microns, the thermosensitive layer has an averagecoverage of about 0.1 to about 2.0 g/m², and the average height of thevalleys on the thermosensitive layer surface is at least 0.1 micronsbelow the average height of the peaks on the thermosensitive layersurface. Such a configuration is especially useful for a plate with asemisolid thermosensitive layer because it allows reduction orelimination of the tackiness and fingerprinting problems.

[0050] An ink and/or fountain solution soluble or dispersible overcoatmay be deposited on top of the thermosensitive layer to, for example,protect the thermosensitive layer from oxygen inhibition, contamination,and/or physical damage during handling, reduce tackiness and blockingtendency, and/or improve the on-press developability. For wet plate, theovercoat preferably comprises a water-soluble polymer, such as polyvinylalcohol (including various water-soluble derivatives of polyvinylalcohol). Various additives, such as surfactant, wetting agent,defoamer, leveling agent, and dispersing agent, can be added into theovercoat formulation to facilitate, for example, the coating ordevelopment process. Various nonionic surfactants and ionic surfactantscan be used. Examples of surfactants useful in the overcoat of thisinvention include polyethylene glycol, polypropylene glycol, andcopolymer of ethylene glycol and propylene glycol, polysiloxanesurfactants, perfluorocarbon surfactants, sodium dioctylsulfosuccinate,sodium dodecylbenzenesulfonate, and ammonium laurylsulfate. Thesurfactant can be added preferably at 0.01 to 40% by weight of theovercoat, more preferably at 0.2 to 15%. The overcoat preferably has acoverage of from 0.001 to 1 g/m², more preferably from 0.002 to 0.45g/m², most preferably from 0.005 to 0.20 g/m².

[0051] For plates with rough and/or porous surface capable of mechanicalinterlocking with a coating deposited thereon, a thin releasableinterlayer soluble or dispersible in ink (for waterless plate) or inkand/or fountain solution (for wet plate) may be deposited between thesubstrate and the thermosensitive layer. Here the substrate surface isrough and/or porous enough and the interlayer is thin enough to allowbonding between the thermosensitive layer and the substrate throughmechanical interlocking. Such a plate configuration is described in U.S.Pat. No. 6,014,929, the entire disclosure of which is herebyincorporated by reference.

[0052] The plate is usually coated on a manufacture line by coating thethermosensitive layer, and optionally the overcoat and/or theinterlayer, on the substrate. The coated plate (which is usually cut tosuitable sizes) is sold as commercial products to be used in thepressroom for imaging and printing. For direct-to-press applications,alternatively, the plate may be directly coated on the plate cylinder ofa lithographic press equipped with digital laser imaging device. Thethermosensitive layer can be coated onto the substrate which is a sheetmaterial mounted on the plate cylinder or is the surface of the platecylinder of the press. A coating device containing the thermosensitivefluid can be mounted on the press. The coating device can coat throughany means, such as slot coating, roller coating, spray coating, andinkjet. The coating fluid can be a solvent or aqueous solution ordispersion, or can be free of solvent or water. For coating free ofsolvent or water, a liquid or semisolid thermosensitive coating materialcan be used. After coating (and optionally further drying), thethermosensitive layer can be exposed with an infrared laser to imagewiseharden the exposed areas. The exposed plate surface can then becontacted with ink and/or fountain solution to remove the non-hardenedareas and to print imaging from the plate (usually through a blanketcylinder) to the receiving medium. The plate substrate can be a sheetmaterial mounted on the plate cylinder, or can be the cylinder surface.Press with the cylinder surface as the substrate can be used forseamless printing. For press using the cylinder surface as the substrateor with a reusable plate substrate, after the completion of printing,the hardened thermosensitive layer may be stripped off by various means,including wiping with a cloth dampened with a solvent or solution orstripping with a blade. Such a stripping process may be performed byhand or with a stripping device mounted on the press. The strippedsubstrate can be re-coated with the thermosensitive layer (andoptionally the overcoat and/or interlayer) to form a thermosensitiveplate for next imaging and printing application.

[0053] For press using the cylinder surface as the substrate or with areusable plate substrate, the thermosensitive layer (and optionallyovercoat and/or interlayer) coating, digital exposure with infraredradiation, on-press development with ink and/or fountain solution,printing to the receiving sheet, and stripping can be performedsequentially and continuously around the rotating plate cylinder so thateach printed sheet can have different imaging. For such an application,the thermosensitive layer must be able to develop quickly upon contactwith the ink and/or fountain solution rollers. Such a process issuitable for variable data printing. When miniaturized, such a systemcan be used for desktop printing, performing similar function as thecurrent laser Xerox printer and inkjet printer.

[0054] The lithographic plate of the present invention can also be usedas a seamless sleeve printing plate. In this option the printing plateis soldered in a cylindrical form. This cylindrical printing plate whichhas a diameter of the plate cylinder diameter is slid onto the platecylinder from one end of the plate cylinder. The seamless sleeveprinting plate can be coated with thermosensitive layer (and optionallythe overcoat and/or interlayer) before or after sliding onto the platecylinder of the press.

[0055] The infrared radiation suitable for exposing the lithographicplate of the instant invention can be from any infrared radiation sourcesuitable for digital imaging. Infrared lasers are preferred infraredradiation sources. Infrared lasers useful for the imagewise exposure ofthe thermosensitive plates of this invention include laser sourcesemitting in the near infrared region, i.e. emitting in the wavelengthrange of from 700 to 1500 nm, and preferably from 750 to 1200 nm.Particularly preferred infrared laser sources are laser diodes emittingaround 830 nm or a NdYAG laser emitting around 1060 nm. The plate isexposed at a laser dosage that is sufficient to cause hardening in theexposed areas but not high enough to cause substantial thermal ablation.The exposure dosage is preferably from 1 to 2000 mJ/cm², more preferablyfrom 5 to 1000 mJ/cm², most preferably from 30 to 500 mJ/cm², dependingon the sensitivity of the thermosensitive layer.

[0056] Laser imaging devices are currently widely availablecommercially. Any device can be used which provides imagewise laserexposure according to digital imaging information. Commonly used imagingdevices include flatbed imager, internal drum imager, and external drumimager. Internal drum imager and external drum imager are preferredimaging devices.

[0057] The plate can be imaged off press or on press. For off-pressimaging, the plate is imagewise exposed with a laser in a plate imagingdevice, and the exposed plate is then mounted on the plate cylinder of alithographic press to be developed with ink (for waterless plate) orwith ink and/or fountain solution (for wet plate) by rotating the presscylinders and contacting the plate with ink and/or fountain solution andto lithographically print images from said plate to the receiving media(such as papers). For on-press imaging, the plate is exposed whilemounted on a lithographic printing press cylinder, and the exposed plateis directly developed on press with ink and/or fountain solution duringinitial press operation and then prints out regular printed sheets. Thisis especially suitable for computer-to-press application in which theplate (or plates, for multiple color press) is directly exposed on theplate cylinder of a press according to computer generated digitalimaging information and, with minimum or no treatment, directly printsout regular printed sheets. For on-press development, good qualityprints should be obtained preferably under 20 initial impressions, andmore preferably under 5 impressions.

[0058] For conventional wet press, usually fountain solution is applied(to contact the plate) first, followed by contacting with ink roller.For press with integrated inking/dampening system, the ink and fountainsolution are emulsified by various press rollers before beingtransferred to the plate as emulsion of ink and fountain solution.However, in this invention, the ink and fountain solution may be appliedat any combination or sequence, as needed for the plate. There is noparticular limitation. The recently introduced single fluid ink by FlinkInk Company, which can be used for printing wet lithographic platewithout the use of fountain solution, can also be used for the on-pressdevelopment and printing of the plate of this invention.

[0059] The plate may be rinsed or applied with an aqueous solution,including water and fountain solution, to remove the water soluble ordispersible overcoat (for plate with an overcoat) and/or to dampenwithout developing the plate, after imagewise exposure and beforeon-press development with ink and/or fountain solution.

[0060] A liquid layer may be applied onto the surface of the plate (withor without an overcoat) before and/or during imaging process to providean in situ oxygen barrier layer during the imaging process to allowfaster photospeed and better curing. The liquid layer can be any liquidmaterial that does not cause substantial adverse effect on the plate.Water, fountain solution, and other aqueous solutions are preferredmaterials for forming the liquid layer for a plate with an oleophilicthermosensitive layer. The liquid layer may be applied from a dampeningroller of a lithographic press with the plate being mounted on the platecylinder during on-press imaging process. The dampening roller can be aregular dampening roller which supplies fountain solution duringprinting or can be a different roller.

[0061] An inert gas (such as nitrogen) may be introduced within thedevice or near the exposure areas during a laser imaging process toreduce oxygen inhibition of free radical polymerization of thethermosensitive layer. The inert gas may be flushed from a nozzlemounted next to the laser head onto the areas being imaged during thelaser imaging process; this is especially useful for external drumimaging devices, including off-press laser imaging devices having anexternal drum and on-press laser imaging devices utilizing platecylinder as the imaging drum.

[0062] This invention is further illustrated by the followingnon-limiting examples of its practice. Unless specified, all the valuesare by weight.

EXAMPLE 1

[0063] An electrochemically roughened, anodized, and polyvinylphosphonic acid treated aluminum sheet was coated using a #6 Meyer rodwith a thermosensitive layer formulation TS-1, followed by drying in anoven at 70° C. for 5 min. TS-1 Component Weight ratios Epon 1031 (Epoxyresin from Shell Chemical Company) 2.114 Cyracure UVR-6110 (Epoxy resinfrom Union Carbide) 3.442 Cyracure UVI-6990 (Cationic initiator from1.387 Union Carbide) Microlith Black C-K (Carbon black dispersed inpolymer 3.750 binder, from Ciba-Geigy) Ethyl acetate 78.590  Acetone10.717 

[0064] The above plate was exposed with an infrared laser plate imagerequipped with laser diodes (8-channels, about 500 mW each) emitting at830 nm with a laser size of about 15 microns (ThermalSetter™, fromOptronics). The plate was placed on the imaging drum and secured withvacuum (and masking tape if necessary). The exposure dosage wascontrolled by the drum speed. The plate was exposed at a laser dosage(about 300-500 mJ/cm²) which is sufficient to cause hardening in theexposed areas but not high enough to cause thermal ablation. Visibleimage pattern (in different tone of black) was seen in the exposedareas.

[0065] The exposed plate was subjected to hand test for on-pressdevelopability. The plate was rubbed back and forth for 10 times with acloth soaked with both fountain solution and ink to check on-pressdevelopability and inking. The plate developed completely under 8 doublerubs. The non-exposed areas of the thermosensitive layer were completelyremoved, and the exposed areas of the thermosensitive layer stayed onthe substrate. The developed plate showed well-inked imaging pattern inthe exposed areas and clean background in the non-exposed areas.

EXAMPLE 2

[0066] An electrochemically roughened, anodized, and polyvinylphosphonic acid treated aluminum sheet was coated using a #6 Meyer rodwith a thermosensitive layer formulation TS-2, followed by drying in anoven at 70° C. for 5 min. TS-2 Component Weight ratios Epon 1031 (Epoxyresin from Shell Chemical Company) 2.326 Cyracure UVR-6110 (Epoxy resinfrom Union Carbide) 3.786 Cyracure UVI-6974 (Sulfonium salt cationicinitiator 0.852 from Union Carbide) CD-1012 (Iodonium salt cationicinitiator from Sartomer 0.252 Company) Neocryl B-728 (Polymeric binderfrom Zeneca) 2.520 IR-140 (Infrared dye from Eastman Kodak) 0.654 FC120(Surfactant from 3M) 0.036 Ethyl acetate 78.825  Acetone 10.749 

[0067] The plate was exposed and hand developed as in EXAMPLE 1. Theexposed plate showed dark-blue color in the exposed areas. The platedeveloped completely under 8 double rubs, with the non-imaging areas ofthe thermal sensitive layer being completely removed. The developedplate showed well-inked imaging pattern, and clean background.

EXAMPLE 3

[0068] An electrochemically grained, anodized, and silicate treatedaluminum substrate (with an Ra of about 0.5 microns) was coated using a#6 Meyer rod with a thermosensitive layer formulation TS-3, followed bydrying in an oven at 80° C. for 5 min. TS-3 Component Weight ratiosNeocryl B-728 (Polymer from Zeneca) 2.73 Sartomer SR-399 (Acrylicmonomer from Sartomer) 6.52 Pluronic L43 (Nonionic surfactant from BASF)0.56 (4-(2-Hydroxytetradecyl-oxy)-phenyl)phenyliodonium 0.50hexafluoroantimonate PINA FK-1026 (Infrared absorbing polymethine dye0.20 from Allied Signal) Acetone 90.2 

[0069] The above plate was exposed with an infrared laser plate imagerequipped with laser diodes emitting at about 830 nm (Pearlsetter™, fromPresstek). The plate was mounted on the imaging drum (external drum) andexposed at a laser dosage of about 600 mJ/cm².

[0070] The plate was tested on a wet lithographic press (AB Dick 360)equipped with integrated inking/dampening system. The exposed plate wasdirectly mounted on the plate cylinder of the press. The press wasstarted for 10 rotations, and the ink roller (carrying emulsion of inkand fountain solution) was then applied to the plate cylinder to rotateuntil the plate showed clean background. The plate cylinder was thenengaged with the blanket cylinder and printed with papers. The printedsheets showed good inking in exposed areas and clean background innon-exposed areas under 10 impressions. The press continued to run for atotal of 100 impressions without showing any wearing (The press stoppedat 100 impressions.).

EXAMPLE 4

[0071] The plate prepared in EXAMPLE 3 was further coated with awater-soluble overcoat OC-1 using a #6 Meyer rod, followed by drying inan oven at 80° C. for 5 min. OC-1 Component Weight ratios Airvol 205(Polyvinyl alcohol from Air Products) 2.00 Zonyl FSO (Perfluorinatedsurfactant from DuPont) 0.02 Water 98.00 

[0072] The overcoated plate was exposed and on-press developed as inEXAMPLE 3. The printed sheets showed good inking in exposed areas andclean background in non-exposed areas under 5 impressions. The platecontinued to run for a total of 100 impressions without showing anywearing (The press stopped at 100 sheets.).

EXAMPLE 5

[0073] In this example, the plate is the same as in EXAMPLE 3 exceptthat a thin releasable interlayer (a water-soluble polymer) isinterposed between the substrate and the thermosensitive layer.

[0074] An electrochemically roughened, anodized, and silicate treatedaluminum sheet was first coated with a 0.2% aqueous solution ofpolyvinyl alcohol (Airvol 540, from Air Products) with a #6 Meyer rod,followed by drying in an oven at 80° C. for 5 min. The polyvinyl alcoholcoated substrate was further coated with the thermosensitive layerformulation TS-3 with a #6 Meyer rod, followed by drying in an oven at80° C. for 5 min.

[0075] The plate was exposed and on-press developed as in EXAMPLE 3. Theprinted sheets showed good inking in exposed areas and clean backgroundin non-exposed areas under 2 impressions. The plate continued to run fora total of 100 impressions without showing any wearing (The pressstopped at 100 sheets.).

EXAMPLE 6

[0076] An electrochemically roughened, anodized, and silicate treatedaluminum sheet was first coated with a 0.1% aqueous solution ofpolyvinyl alcohol (Airvol 540, from Air Products) with a #6 Meyer rod,followed by drying in an oven at 80° C. for 5 min. The polyvinyl alcoholcoated substrate was further coated with the thermosensitive layerformulation TS-4 with a #6 Meyer rod, followed by drying in an oven at80° C. for 5 min. TS-4 Component Weight ratios Neocryl B-728 (Polymerfrom Zeneca) 2.73 Sartomer SR-399 (Acrylic monomer from Sartomer) 6.52Pluronic L43 (Nonionic surfactant from BASF) 0.56 Cyracure 6974 (Mixedtriarylsulfonium 1.00 hexafluoroantimonate from Union Carbide) PINAFK-1026 (Infrared absorbing polymethine dye 0.20 from Allied Signal)Acetone 90.2 

[0077] The thermosensitive layer coated plate was further coated with awater-soluble overcoat OC-2 using a #6 Meyer rod, followed by drying inan oven at 80° C. for 5 min. OC-2 Component Weight ratios Airvol 205(Polyvinyl alcohol from Air Products) 0.2  Dioctyl sulfosuccinate sodiumsalt (surfactant) 0.01 Water 99.8 

[0078] The plate was exposed with an infrared laser plate imagerequipped with laser diodes emitting at about 830 nm (Dimension 400, fromPresstek). The plate was mounted on the imaging drum and exposed at alaser dosage of about 450 mJ/cm².

[0079] The exposed plate was on-press developed as in EXAMPLE 3. Theprinted sheets showed good inking in exposed areas and clean backgroundin non-exposed areas under 2 impressions. The plate continued to run fora total of 200 impressions without showing any wearing (The pressstopped at 200 sheets.).

EXAMPLE 7

[0080] This example illustrates imagewise exposure with an infraredradiation from a conventional light source.

[0081] The same plate as in EXAMPLE 6 was exposed with an infrared lamp(from General Electric) under a negative photomask made of aluminum foilfor 4 minutes. The infrared light source was positioned at 4 inches awayfrom the photomask-covered plate during the exposure.

[0082] The exposed plate was on-press developed as in EXAMPLE 3. Theprinted sheets showed good inking in exposed areas and clean backgroundin non-exposed areas under 2 impressions. The plate continued to run fora total of 200 impressions without showing any wearing (The pressstopped at 200 sheets.).

EXAMPLE 8

[0083] An electrochemically roughened, anodized, and silicate treatedaluminum sheet was first coated with a 0.1% aqueous solution ofpolyvinyl alcohol (Airvol 540, from Air Products) with a #6 Meyer rod,followed by drying in an oven at 80° C. for 5 min. The polyvinyl alcoholcoated substrate was further coated with the thermosensitive layerformulation TS-5 with a #6 Meyer rod, followed by drying in an oven at80° C. for 5 min. TS-5 Component Weight ratios Neocryl B-728 (Polymerfrom Zeneca) 2.73 Sartomer SR-399 (Acrylic monomer from Sartomer) 6.52Pluronic L43 (Nonionic surfactant from BASF) 0.56(4-(2-Hydroxytetradecyl-oxy)-phenyl)phenyliodonium 0.70hexafluoroantimonate2,4-Bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen- 0.301-yl]-s-triazine ADS-830AT (Infrared absorbing cyanine dye from 0.10American Dye Source) Acetone 90.2 

[0084] The thermosensitive layer coated plate was further coated with awater-soluble overcoat OC-3 using a #6 Meyer rod, followed by drying inan oven at 80° C. for 5 min. OC-3 Component Weight ratios Airvol 205(Polyvinyl alcohol from Air Products) 2.00 Dioctyl sulfosuccinate sodiumsalt (surfactant) 0.08 Water 98.0 

[0085] The plate was exposed with an infrared laser plate imagerequipped with laser diodes emitting at about 830 nm (Dimension 400, fromPresstek). The plate was mounted on the imaging drum and exposed at alaser dosage of about 300 mJ/cm². The exposed areas showed yellow-brownimaging pattern, in contrast to the light green non-imaged areas.

[0086] The exposed plate was on-press developed as in EXAMPLE 3. Theprinted sheets showed good inking in exposed areas and clean backgroundin non-exposed areas under 2 impressions. The plate continued to run fora total of 200 impressions without showing any wearing (The pressstopped at 200 sheets.).

EXAMPLE 9

[0087] An electrochemically roughened, anodized, and silicate treatedaluminum sheet was first coated with a 0.1% aqueous solution ofpolyvinyl alcohol (Airvol 540, from Air Products) with a #6 Meyer rod,followed by drying in an oven at 80° C. for 5 min. The polyvinyl alcoholcoated substrate was further coated with the thermosensitive layerformulation TS-6 with a #6 Meyer rod, followed by drying in an oven at80° C. for 5 min. TS-6 Component Weight ratios Neocryl B-728 (Polymerfrom Zeneca) 2.73 Sartomer SR-399 (Acrylic monomer from Sartomer) 6.52Pluronic L43 (Nonionic surfactant from BASF) 0.56(4-(2-Hydroxytetradecyl-oxy)-phenyl)phenyliodonium 1.00hexafluoroantimonate ADS-830AT (Infrared absorbing cyanine dye from 0.02American Dye Source) Acetone 90.2 

[0088] The thermosensitive layer coated plate was further coated with awater-soluble overcoat OC-3 using a #6 Meyer rod, followed by drying inan oven at 80° C. for 5 min.

[0089] The plate was exposed with an infrared laser plate imagerequipped with laser diodes emitting at about 830 nm (Dimension 400, fromPresstek). The plate was mounted on the imaging drum and exposed at alaser dosage of about 300 mJ/cm².

[0090] The exposed plate was on-press developed as in EXAMPLE 3. Theprinted sheets showed good inking in the exposed areas and cleanbackground in the non-exposed areas under 2 impressions. The platecontinued to run for a total of 200 impressions without showing anywearing (The press stopped at 200 sheets.).

EXAMPLE 10

[0091] An electrochemically roughened, anodized, and silicate treatedaluminum sheet was first coated with a 0.1% aqueous solution ofpolyvinyl alcohol (Airvol 540, from Air Products) with a #6 Meyer rod,followed by drying in an oven at 80° C. for 5 min. The polyvinyl alcoholcoated substrate was further coated with the thermosensitive layerformulation TS-7 with a #6 Meyer rod, followed by drying in an oven at80° C. for 5 min. TS-7 Component Weight ratios Neocryl B-728 (Polymerfrom Zeneca) 2.73 Sartomer SR-399 (Acrylic monomer from Sartomer) 6.52Pluronic L43 (Nonionic surfactant from BASF) 0.562,4-Bis(trichloromethyl)-6-[(4-ethoxyethylenoxy)-phen- 1.001-yl]-s-triazine ADS-830AT (Infrared absorbing cyanine dye from 0.10American Dye Source) Acetone 90.0 

[0092] The thermosensitive layer coated plate was further coated with awater-soluble overcoat OC-2 using a #6 Meyer rod, followed by drying inan oven at 80° C. for 5 min.

[0093] The plate was exposed with an infrared laser plate imagerequipped with laser diodes emitting at about 830 nm (Trendetter fromCreoScitex). The plate was mounted on the imaging drum and exposed at alaser dosage of about 300 mJ/cm². The exposed areas showed glossier butessentially colorless imaging pattern, in contrast to the less glossynon-imaged areas.

[0094] The exposed plate was on-press developed as in EXAMPLE 3. Theprinted sheets showed good inking in exposed areas and clean backgroundin non-exposed areas under 2 impressions. The plate continued to run fora total of 200 impressions without showing any wearing (The pressstopped at 200 sheets.).

EXAMPLE 11

[0095] An electrochemically grained, anodized, and silicate treatedaluminum substrate was coated using a #6 Meyer rod with athermosensitive layer formulation TS-8, followed by drying in an oven at80° C. for 5 min. TS-8 Component Weight ratios Neocryl B-728 (Polymerfrom Zeneca) 2.73 Sartomer SR-399 (Acrylic monomer from Sartomer) 6.52Pluronic L43 (Nonionic surfactant from BASF) 0.56(4-(2-Hydroxytetradecyl-oxy)-phenyl)phenyliodonium 1.00hexafluoroantimonate PINA FK-1151 (Infrared absorbing polymethine dye0.30 from Allied Signal) Acetone 90.2 

[0096] Five sheets of the above thermosensitive layer coated plates wereprepared. The plates were further coated with a water-soluble overcoatfrom a solution consisting of Airvol 205 (polyvinyl alcohol from AirProducts) in water with addition of Zonyl FSO (Perfluorinated surfactantfrom DuPont) at about 0.02% by weight of the solution using a #6 Meyerrod, followed by drying in an oven at 80° C. for 5 min. The solutionconcentration and coating coverage are listed in Table 1.

[0097] The above plates were each exposed with an infrared laser plateimager equipped with laser diodes emitting at about 830 nm (Trendetterfrom CreoScitex). The plate was mounted on the imaging drum and exposedat a laser dosage of about 400 mJ/cm².

[0098] The plates were tested on a wet lithographic press (AB Dick 360)equipped with integrated inking/dampening system. The exposed plate wasdirectly mounted on the plate cylinder of the press. The press wasstarted for 10 rotations, and the ink roller (carrying emulsion of inkand fountain solution) was then applied to the plate cylinder to rotatefor 10 rotations. The plate cylinder was then engaged with the blanketcylinder and printed to papers. The press continued to run for a totalof 200 impressions. The press test results are listed in Table 1. TABLE1 Overcoat Roll-up to Roll-up to Wearing Overcoat coverage cleanbackground good inking at 200 polymer (g/m²) (Rotations) (Rotations)impressions No overcoat None 40  1 No Airvol 205 0.02 10  1 No Airvol205 0.20 10  1 No Airvol 205 0.40 10 20 No Airvol 205 1.00 10 80 No

I claim:
 1. A negative lithographic printing plate capable of on-pressdevelopment with ink and/or fountain solution, comprising on a substratea thermosensitive layer; said thermosensitive layer comprising (i) acationic polymerizable monomer, (ii) a cationic initiator, and (iii) aninfrared absorber; wherein said thermosensitive layer is capable ofhardening upon exposure to an infrared radiation, and soluble ordispersible in ink and/or fountain solution; and at least the hardenedareas of said thermosensitive layer exhibit an affinity or aversionsubstantially opposite to the affinity or aversion of said substrate toat least one printing liquid selected from the group consisting of inkand an abhesive fluid for ink.
 2. The lithographic plate of claim 1wherein said substrate is hydrophilic, said thermosensitive layer isoleophilic, said monomer is an epoxy or vinyl ether monomer having atleast one epoxy or vinyl ether functional group, said cationic initiatoris a free acid generator, and said infrared absorber is an infraredabsorbing dye.
 3. The lithographic plate of claim 2 wherein saidthermosensitive layer further comprises a free radical polymerizableethylenically unsaturated monomer having at least one terminal ethylenicgroup, and a free radical initiator; and is capable of both cationic andfree radical polymerizations upon exposure to the infrared radiation. 4.The lithographic plate of claim 2 wherein said cationic initiator iscapable of generating both free acid and free radical, and saidthermosensitive layer further comprises a free radical polymerizableethylenically unsaturated monomer having at least one terminal ethylenicgroup and is capable of both cationic and free radical polymerizationsupon exposure to the infrared radiation.
 5. The lithographic plate ofclaim 2 wherein said epoxy or vinyl ether monomer has both epoxy orvinyl ether group and free radical polymerizable ethylenic group, saidcationic initiator is capable of generating both free acid and freeradical, and said thermosensitive layer is capable of both cationic andfree radical polymerizations upon exposure to the infrared radiation. 6.A negative lithographic printing plate capable of on-press developmentwith ink and/or fountain solution, comprising on a substrate athermosensitive layer; said thermosensitive layer being capable ofhardening through free radical or cationic polymerization upon exposureto an infrared radiation, on-press developable with ink and/or fountainsolution, and exhibiting an affinity or aversion substantially oppositeto the affinity or aversion of said substrate to at least one printingliquid selected from the group consisting of ink and an abhesive fluidfor ink; wherein said substrate has a roughened surface comprising peaksand valleys, and said thermosensitive layer is substantially conformallycoated on the roughened substrate surface so that the surface of saidthermosensitive layer has peaks and valleys substantially correspondingto the major peaks and valleys of the substrate microscopic surface; andsaid substrate has an average surface roughness Ra of from 0.2 to 2.0microns, said thermosensitive layer has an average coverage of from 0.1to 2.0 g/m², and the average height of the valleys on thethermosensitive layer surface is at least 0.1 microns below the averageheight of the peaks on the thermosensitive layer surface.
 7. Thelithographic plate of claim 6 wherein the average height of the valleyson the thermosensitive layer surface is at least 0.1 microns below theaverage height of the major peaks on the substrate surface.
 8. Thelithographic plate of claim 6 wherein the average height of the valleyson the thermosensitive layer surface is at least 0.3 microns below theaverage height of the peaks on the thermosensitive layer surface.
 9. Thelithographic plate of claim 6 wherein the average height of the valleyson the thermosensitive layer surface is at least 0.5 microns below theaverage height of the peaks on the thermosensitive layer surface. 10.The lithographic plate of claim 6 wherein said substrate has an averagesurface roughness Ra of from 0.3 to 1.0 microns, and saidthermosensitive layer has an average coverage of from 0.2 to 1.4 g/m².11. The lithographic plate of claim 6 wherein said substrate has anaverage surface roughness Ra of from 0.4 to 0.8 microns, and saidthermosensitive layer has an average coverage of from 0.4 to 1.1 g/m².12. The lithographic plate of claim 6 wherein said substrate ishydrophilic; and said thermosensitive layer is oleophilic and comprisesan epoxy or vinyl ether monomer having at least one epoxy or vinyl etherfunctional group, a cationic initiator, and an infrared absorbing dye.13. The lithographic plate of claim 6 wherein said substrate ishydrophilic; and said thermosensitive layer is oleophilic and comprisesa free radical polymerizable ethylenically unsaturated monomer having atleast one terminal ethylenic group, a free-radical initiator, and aninfrared absorbing dye.
 14. The lithographic plate of claim 6 whereinsaid substrate is hydrophilic; and said thermosensitive layer isoleophilic and comprises an oleophilic polymeric binder, a(meth)acrylate monomer, a free-radical initiator, and an infraredabsorbing dye.
 15. The lithographic plate of claim 6 further including areleasable interlayer interposed between the substrate and thethermosensitive layer, said releasable interlayer being soluble ordispersible in ink and/or fountain solution; wherein the substratecomprises rough and/or porous surface capable of mechanical interlockingwith a coating deposited thereon, and the interlayer is substantiallyconformally coated on the microscopic surfaces of the substrate and isthin enough in thickness, to allow bonding between the thermosensitivelayer and the substrate through mechanical interlocking.
 16. Thelithographic plate of claim 6 further including an ink and/or fountainsolution soluble or dispersible overcoat on the thermosensitive layer.17. A negative lithographic printing plate capable of on-pressdevelopment with ink and/or fountain solution, comprising on ahydrophilic substrate an oleophilic thermosensitive layer; saidthermosensitive layer comprising (i) a free radical polymerizableethylenically unsaturated monomer having at least one terminal ethylenicgroup, (ii) a free radical initiator, (iii) an infrared absorbing dye,and (iv) a nonionic surfactant at 1.0 to 30% by weight of thethermosensitive layer; wherein said thermosensitive layer is capable ofhardening upon exposure to an infrared radiation, and soluble ordispersible in ink and/or fountain solution.
 18. The lithographic plateof claim 17 wherein said nonionic surfactant is selected from the groupconsisting of block copolymer of propylene oxide and ethylene oxide,polyethylene glycol, and polyalkoxylated polyether.
 19. The lithographicplate of claim 17 wherein said nonionic surfactant is at 2.0 to 20% byweight of the thermosensitive layer.
 20. The lithographic plate of claim17 wherein said nonionic surfactant is at 4.0 to 15% by weight of thethermosensitive layer.
 21. The lithographic plate of claim 17 whereinsaid thermosensitive layer further comprises a polymeric binder.
 22. Anegative lithographic printing plate capable of on-press developmentwith ink and fountain solution, comprising in order: (i) a hydrophilicsubstrate, (ii) an oleophilic thermosensitive layer, and (iii) a watersoluble or dispersible overcoat at a coverage of from 0.001 to 0.450g/m²; wherein said thermosensitive layer is capable of hardening uponexposure to an infrared radiation and on-press developable with inkand/or fountain solution.
 23. The lithographic plate of claim 22 whereinsaid overcoat has a coverage of from 0.002 to 0.35 g/m².
 24. Thelithographic plate of claim 22 wherein said overcoat has a coverage offrom 0.005 to 0.20 g/m².
 25. The lithographic plate of claim 22 whereinsaid thermosensitive layer comprises a free radical polymerizableethylenically unsaturated monomer having at least one terminal ethylenicgroup, a free-radical initiator, and an infrared absorbing dye; and saidovercoat comprises a water-soluble polymer.
 26. The lithographic plateof claim 22 wherein said plate further includes a water soluble ordispersible interlayer interposed between the substrate and thethermosensitive layer; wherein the substrate comprises rough and/orporous surface capable of mechanical interlocking with a coatingdeposited thereon, and the interlayer is substantially conformallycoated on the microscopic surfaces of the substrate and is thin enoughin thickness, to allow bonding between the thermosensitive layer and thesubstrate through mechanical interlocking.
 27. A negative lithographicprinting plate capable of on-press development with ink and fountainsolution, comprising in order: (a) a hydrophilic substrate with roughand/or porous surface; (b) a water soluble or dispersible interlayer;and (c) an oleophilic thermosensitive layer capable of hardening uponexposure to an infrared radiation and on-press developable with inkand/or fountain solution, said thermosensitive layer comprising (i) afree radical polymerizable ethylenically unsaturated monomer having atleast one terminal ethylenic group, (ii) a free radical initiator, and(iii) an infrared absorbing dye; wherein (d) the substrate surface isrough and/or porous enough and said interlayer is thin enough inthickness to allow bonding between said thermosensitive layer and saidsubstrate through mechanical interlocking.
 28. The lithographic plate ofclaim 27 wherein said interlayer has an average coverage of from 0.001to 0.100 g/m² and said substrate has an average surface roughness Ra offrom 0.3 to 1.0 microns.
 29. The lithographic plate of claim 27 whereinsaid interlayer comprises a water-soluble polymer.
 30. A negativelithographic printing plate comprising on a hydrophilic substrate athermosensitive layer; said thermosensitive layer comprising (i) a freeradical polymerizable ethylenically unsaturated monomer having at leastone terminal ethylenic group, (ii) a free radical initiator, (iii) aninfrared absorbing dye, and (iv) optionally a polymeric binder; whereinsaid thermosensitive layer is hydrophilic, on-press developable with inkand/or fountain solution, and capable of hardening and becomingoleophilic upon exposure to an infrared radiation; and at least one ofthe monomer and polymer in the thermosensitive layer has hydrophilicsalt functional groups.
 31. The lithographic plate of claim 30 whereinsaid hydrophilic salt functional group is capable of thermaldecomposition.
 32. The lithographic plate of claim 30 wherein saidsubstrate has a roughened surface comprising peaks and valleys, and saidthermosensitive layer is substantially conformally coated on theroughened substrate surface so that the surface of said thermosensitivelayer has peaks and valleys substantially corresponding to the majorpeaks and valleys of the substrate microscopic surface; and saidsubstrate has an average surface roughness Ra of 0.2 to 2.0 microns,said thermosensitive layer has an average coverage of 0.1 to 2.0 g/m²,and the average height of the valleys on the thermosensitive layersurface is at least 0.1 microns below the average height of the peaks onthe radiation-sensitive layer surface.
 33. The lithographic plate ofclaim 32 wherein said radiation-sensitive layer is semisolid, capable offorming finger prints by gentle pressing with fingers when coated on aflat surface; and the radiation-sensitive layer coverage is low enoughand the substrate average surface roughness is high enough so that theplate does not form visible fingerprints by gentle pressing with fingerson the photosensitive layer surface.
 34. The lithographic plate of claim30 further including a water soluble or dispersible overcoat on thethermosensitive layer.
 35. A method of lithographically printing imageson a receiving medium, comprising in order: (a) providing a negativelithographic plate comprising on a hydrophilic substrate athermosensitive layer comprising (i) a free radical polymerizableethylenically unsaturated monomer having at least one terminal ethylenicgroup, (ii) a free radical initiator, (iii) an infrared absorbing dye,and (iv) optionally a polymeric binder; wherein at least one of themonomer and polymer in the thermosensitive layer has hydrophilic saltfunctional groups; and said thermosensitive layer is hydrophilic,on-press developable with ink and/or fountain solution, and capable ofhardening and becoming oleophilic upon exposure to an infraredradiation; (b) imagewise exposing the plate with the infrared radiationto render the thermosensitive layer hardened and more oleophilic in theexposed areas; and (c) contacting said exposed plate with ink andfountain solution on a lithographic press to lithographically printimages from said plate to the receiving medium, wherein saidthermosensitive layer is quickly or gradually removed with ink and/orfountain solution during the initial printing operation.
 36. The methodof claim 35 wherein said hydrophilic salt functional group is capable ofthermal decomposition and said infrared radiation is an infrared laser.37. The method of claim 35 wherein said plate is mounted on a platecylinder of a lithographic press for the imagewise exposure, on-pressdevelopment with ink and/or fountain solution, and lithographicprinting.